1. Field of the Invention
The present invention concerns an ultrasonic scanner and method for imaging the surface of a part. The present invention is particularly useful in the energy production area where location of defects in equipment is usually difficult using any nondestructive analysis procedure presently in the art.
2. Description of Related Art
The energy of sound waves is useful for checking the condition of materials. For example, ultrasonic energy may by used to detect the presence of flaws. Ultrasonics is advantageous over other destructive methods of testing materials for defects. In destructive testing, defects are made apparent by stressing the part, for example, by bending or tension until any cracks present on the part break open. By comparison, ultrasound is at such a low intensity that the part does not become damaged.
During ultrasonic testing, ultrasonic waves are transmitted from a transmitter on a probe into the part and then returning waves are received for analysis of the information it carries. In this manner, inspection data is obtained over a defined spatial sampling grid on the surface of a three-dimensional part. This data is stored in a computer's memory for subsequent analysis. The sound pressure distribution of the reflected waves are transferred into a visual image. During analysis, the spatial relationships between reflections of ultrasound from within the part are readily apparent in the image. For general information regarding ultrasonic instrumentation, See J. Krautkramer, et al., Ultrasonic Testing of Materials, 4th Ed. Springer-Verlag, N.Y. 1990 and D. Christensen, Ultrasonic Bioinstrumentation, John Wiley & Sons, Inc., N.Y., 1988.
Ultrasonic imaging requires a method to track the position of the transmitting probe such that the system can recognize when the probe is at a spatial sampling point and to obtain UT data there. Probe position feedback is often accomplished through position encoders mounted to a track assembly which is itself mounted to the part, See, for example, U.S. Pat. No. 4,700,045.
In the field of part inspection, the object to be tested often includes many non-uniform shapes and sizes, such as nozzles, valves, etc. Scanners which include track assemblies suffer from significant limitations in imaging such complex surfaces. Each track assembly can operate on at most a narrow range of part geometries. Therefore, fabrication of a special purpose track assembly is required for each new complex part to be inspected. Development of these track assemblies is an expensive and time consuming process. In addition, track assemblies generally restrict the motion of the probe to linear trajectories. In use, this track scanner is moved linearly followed by orthogonal increments and repeat of the linear motion. But any installed projection on the part surface limits the ability of the track assembly to complete the desired scan.
Some scanners are not mounted on a track, as in the medical diagnostics industry. However, these ultrasonic devices collect only a limited amount of data and are not efficient in imaging complex parts. These scanners obtain two-dimensional information about the position of the probe, and thus collect only two-dimensional data from the part being inspected. Computers fill-in missing information to create a three-dimensional image. Reconstruction requires sophisticated gap-filling interpolation algorithms, image resampling and image enhancements. See, for example, Watkin, et al., Three-dimensional Reconstruction and Enhancement of Arbitrarily Oriented and Positioned 2D Medical Ultrasonic Images, 1993 Canadian Conference on Electrical and Computer Engineering, pp. 1188-1195. Such reconstructed three-dimensional images lack accuracy.
Similarly, in Martin, et al. U.S. Pat. No. 5,398,691 a free standing probe is made to rotate in a two-dimensional coordinate system and is translated into three-dimensions relative to the space defined by a magnetic field generator. On the other hand, in the present invention, the probe is moved without constraint in three dimensions and the as measured probe location is used by the system software to control the inspection data acquisition process. The present invention has the advantage, therefore, that data acquisition is unconstrained by the three dimensional configuration of the part nor by probe motion and trajectory.
All references, articles, patents, patent applications, standards and the like cited herein are incorporated herein by reference in their entirety.
There is, therefore, a continuing need for ultrasonic scanners and methods which allow for accurate inspection of complex parts. The scanners should collect three-dimensional data which can be conveniently converted to a detailed two-dimensional image. Furthermore, the probe position should be monitored in a configuration which avoids the necessity of track assemblies. The present invention accomplishes these objectives.